Highly-oxidizing Au@MnO nanozymes mediated homogeneous electrochemical detection of organophosphorus independent of dissolved oxygen.

Traditional oxidase-like (OXD) nanozymes rely primarily on O-mediated superoxide anion (O) process for catalytic oxidation and organophosphorus (Ops) detection. While during the actual detection process, the concentration of O is inconstant that can be easily changed with the external environment, distorting detection results. Herein, highly-oxidizing Au@MnO nanozymes with core-shell nanostructure are designed which trigger substantial electron transfer from inner Au core to outer ultrathin MnO layer. According to experimental and theoretical calculations, the core-shell nanostructure and ultrathin MnO of Au@MnO result in the large surface defects, high oxygen vacancies and Mn ratios. The specially structured Au@MnO nanozymes are therefore highly-oxidizing and the catalytic oxidation can be completed merely through electrons transferring instead of the O-mediated O process. Based on this, an oxygen independent and ultrasensitive nanozyme-based sensor is established using homogeneous electrochemistry (HEC), its Ops is detected at a LOD of 0.039 ng mL. Combined with the UV-vis spectrum of 3,3',5,5'-tetramethylbenzidine (TMB), the linear discriminant analysis of five Ops i.e., Ethion, Omethoate, Diazinon, Chlorpyrifos methyl and Dipterex has achieved superior discrimination results. Therefore, HEC based on strong oxidizing nanozymes provide a new avenue for the development of high-performance electrochemical sensors and demonstrate potential applicability to pesticide residue determination in real samples.